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67. Moire Band Structures of the Double twisted Few Layer Graphene

Author

Liang, Miao, Xiao, Meng-Meng, Ma, Zhen, and Gao, Jin-Hua

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Very recently, unconventional superconductivity has been observed in the double twisted trilayer graphene (TLG), where three monolayer graphene (MLG) are stacked on top of each other with two twist angles [J. M. Park, et al., Nature 590, 249 (2021); Z. Hao, et al., Science 371, 1133 (2021); X. Zhang, et al., Phys. Rev. Lett.127, 166802 (2021)]. When some of MLGs in the double twisted TLG are replaced by bilayer graphene (BLG), we get a new family of double twisted moire heterostructure, namely double twisted few layer graphene (DTFLG). In this work, we theoretically investigate the moire band structures of the DTFLGs with diverse arrangements of MLG and BLG. We find that, depending on the relative rotation direction of the two twist angles (alternate or chiral twist) and the middle van der Waals (vdW) layer (MLG or BLG), a general (X+Y+Z)-DTFLG can be classified into four categories, i.e. (X+1+Z)-ATFLG, (X+2+Z)-ATFLG, (X+1+Z)-CTFLG and (X+2+Z)-CTFLG, each of which has its own unique band structure. Here, X, Y, Z denote the three vdW layers, i.e. MLG or BLG. Interestingly, the (X+1+Z)-ATFLGs have a pair of perfect flat bands at the magic angle about $1.54^\circ$ coexisting with a pair of linear or parabolic bands, which is quite like the double twisted TLG. Meanwhile, when the twist angle is smaller than a "magic angle" $1.70^\circ$, the (X+2+Z)-CTFLGs can have two isolated narrow bands at $E_f$ with band width less than 5 meV. The influence of electric field and the topological features of the moire bands have been studied as well. Our work indicates that the DTFLGs, especially the (X+1+Z)-ATFLG and (X+2+Z)-CTFLG, are promising platforms to study the moire flat band induced novel correlation and topological effects., Comment: 13 pages, 10 figures

Published
2021
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74. Profiling the responsiveness of focal adhesions of human cardiomyocytes to extracellular dynamic nano-topography.

Author

Shi, Huaiyu, Wu, Xiangjun, Sun, Shiyang, Wang, Chenyan, Vangelatos, Zacharias, Ash-Shakoor, Ariel, Grigoropoulos, Costas, Mather, Patrick, Henderson, James, and Ma, Zhen

Subjects
Costamere, Dynamic mechanobiology, Focal adhesion, Human induced pluripotent stem cells, Shape memory polymer, Stimuli-responsive biomaterials
Abstract

Focal adhesion complexes function as the mediators of cell-extracellular matrix interactions to sense and transmit the extracellular signals. Previous studies have demonstrated that cardiomyocyte focal adhesions can be modulated by surface topographic features. However, the response of focal adhesions to dynamic surface topographic changes remains underexplored. To study this dynamic responsiveness of focal adhesions, we utilized a shape memory polymer-based substrate that can produce a flat-to-wrinkle surface transition triggered by an increase of temperature. Using this dynamic culture system, we analyzed three proteins (paxillin, vinculin and zyxin) from different layers of the focal adhesion complex in response to dynamic extracellular topographic change. Hence, we quantified the dynamic profile of cardiomyocyte focal adhesion in a time-dependent manner, which provides new understanding of dynamic cardiac mechanobiology.

Published
2022

75. Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr$_3$

Author

Cai, Zhengwei, Bao, Song, Gu, Zhao-Long, Gao, Yi-Peng, Ma, Zhen, Shangguan, Yanyan, Si, Wenda, Dong, Zhao-Yang, Wang, Wei, Wu, Yizhang, Lin, Dongjing, Wang, Jinghui, Ran, Kejing, Li, Shichao, Adroja, Devashibhai, Xi, Xiaoxiang, Yu, Shun-Li, Wu, Xiaoshan, Li, Jian-Xin, and Wen, Jinsheng

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

Topological magnons are bosonic analogues of topological fermions in electronic systems. They have been studied extensively by theory but rarely realized by experiment. Here, by performing inelastic neutron scattering measurements on single crystals of a two-dimensional ferromagnet CrBr$_3$, which was classified as Dirac magnon semimetal featured by the linear bands crossing at the Dirac points, we fully map out the magnetic excitation spectra, and reveal that there is an apparent gap of $\sim$3.5~meV between the acoustic and optical branches of the magnons at the K point. By collaborative efforts between experiment and theoretical calculations using a five-orbital Hubbard model obtained from first-principles calculations to derive the exchange parameters, we find that a Hamiltonian with Heisenberg exchange interactions, next-nearest-neighbor Dzyaloshinskii-Moriya (DM) interaction, and single-ion anisotropy is more appropriate to describe the system. Calculations using the model show that the lower and upper magnon bands separated by the gap exhibit Chern numbers of $\pm1$. These results indicate that CrBr$_3$ is a topological magnon insulator, where the nontrivial gap is a result of the DM interaction., Comment: Version as published in PRB Letter, main text 7 pages, supplementary materials 6 pages

Published
2021
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94. High-density lipoprotein regulates angiogenesis by long non-coding RNA HDRACA

Author

Mo, Zhi-Wei, Peng, Yue-Ming, Zhang, Yi-Xin, Li, Yan, Kang, Bi-Ang, Chen, Ya-Ting, Li, Le, Sorci-Thomas, Mary G., Lin, Yi-Jun, Cao, Yang, Chen, Si, Liu, Ze-Long, Gao, Jian-Jun, Huang, Zhan-Peng, Zhou, Jia-Guo, Wang, Mian, Chang, Guang-Qi, Deng, Meng-Jie, Liu, Yu-Jia, Ma, Zhen-Sheng, Hu, Zuo-Jun, Dong, Yu-Gang, Ou, Zhi-Jun, and Ou, Jing-Song

Published
2023
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99. Doubled Moir\'{e} Flat Bands in Double-twisted Few Layer Graphite

Author

Ma, Zhen, Li, Shuai, Lu, Ming, Xu, Dong-Hui, Gao, Jin-Hua, and Xie, X. C.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

We study the electronic structure of a double-twisted few layer graphite (DTFLG), which consists of three few layer graphite (FLG), i.e. ABA-stacked graphene multilayer, stacked with two twist angles. We consider two categories of DTFLG, alternately twisted case and chirally twisted one, according to the rotation direction of the two twist angles. We show that, once the middle FLG of DTFLG is not thinner than trilayer, both kinds of DTFLG can remarkably host two pairs of degenerate moir\'{e} flat bands (MFBs) at $E_f$, twice that of the magic angle twisted bilayer graphene (TBG). The doubled MFBs of DTFLG lead to doubled DOS at $E_f$, which implies much stronger correlation effects than the TBG. The degeneracy of MFBs can be lifted by a perpendicular electric field, and the isolated MFBs have nonzero valley Chern number. We also reveal the peculiar wave function patterns of the MFBs in the DTFLG. Our results establish a new family of moir\'{e} systems that have the much larger DOS at $E_f$, and thus possible much stronger correlation effects., Comment: 6 pages, 4 figures

Published
2021
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